Application not exist error on POST request to graph.user.messages method. How to solve?

Question

Python

The code:

import requests
import json
group_access_token = "token here"
url = " https://api.ok.ru/graph/me/messages/?access_token= " + group_access_token
data = {"recipient":
{
"user_id": "user: 571289866623"
},
"message":
{
"text":"Hello"
}
}
headers = {'Content-type': 'application/json;charset=utf-8'}
r = requests.post(url, data=json .dumps(data), headers=headers)
print(r.text)

Error:

{"error_code":2000,"error_msg":"GRAPH_PARAM_ACCESS_TOKEN : Application not exist","error_data":null}

Explanation:

The token was received several times according to the instructions in the documentation. I checked and so on, but the error is the same.